Precision resistors are employed in semiconductor circuits including analog devices and radio frequency (RF) devices as a circuit component. Many applications require a well-defined resistance value within a narrow specification range including, for example, a tuning circuit requiring a high Q factor. However, fabrication of high precision resistors is difficult since semiconductor manufacturing processes are prone to process variations such as variations in lithographic critical dimensions and thickness variations in deposited films.
Since statistical variations in processing parameters are inherent in semiconductor devices, manufacture of a resistor having a resistance within a predefined resistance value with a narrow specification range poses a particular challenge. A prior art precision resistor structure includes a network of resistor components connected with programmable electrical fuses. However, such prior art precision resistor structures require a plurality of circuits, each including a programming transistor circuit, a programmable electrical fuse that may be programmed, for example, by electromigration, and a resistor component having a constant resistance. In such applications, the electrical fuses cannot be employed as a resistor since the variations in the programmed electrical fuse has significant statistical variation, and thus, the value of resistance of a programmed electrical fuse is not predictable. Any change in the resistance of the prior art precision resistor structures is effected by connection or disconnection of a resistor component having a constant resistance value irrespective of programming of the electrical fuse. In other words, the electrical fuses and the resistor are two distinct circuit components that are not integrated with each other. Since separate areas are required for the resistor components and electrical fuses, prior art precision resistor structures require a large circuit area.
In view of the above, there exists a need for a programmable resistor structure providing a programmable resistance with a small foot print area for semiconductor applications.